docs: def write_all_sequences_file(self, outname, outdir=None):
          """Write all the stored sequences as a single FASTA file. By default, sets IDs to model gene IDs.
  
          Args:
              outname (str): Name of the output FASTA file without the extension
              outdir (str): Path to output directory for the file, default is the sequences directory
  
          """
  
          if not outdir:
              outdir = self.sequence_dir
              if not outdir:
                  raise ValueError('Output directory must be specified')
  
          outfile = op.join(outdir, outname + '.faa')
          SeqIO.write(self.sequences, outfile, "fasta")
  
          log.info('{}: wrote all protein sequences to file'.format(outfile))
          return outfile